Method and arrangement for diminishing noise in vacuum tubes



June 24, 1930. w, sc R 1,765,542

METHOD AND ARRANGEMENT FOR DIMINISHING NOISE IN VACUUM TUBES Filed Oct.28, 1924 INVENTOR WALTER SCHAFFER TORNEY Patented June 24, 1930 UNITED STATES PATENT, OFFICE WALTER SCHA'FFER, OF BERLIN, GERMANY, ASSIGNOR TO GESELLSOHAFT FER DRAHT- LOSE TELEGRAPHIE M. B. H., OF BERLIN, GERMANY, A. CORPORATION OF GERMANY METHOD AND ARRANGEMENT FOR DIMINISHING NOISE IN VACUUM TUBES Application filed October 28, 1924, Serial No. 746,268, and in Germany December 18, 1923.

My invention relates to a method and means for diminishing and eliminating the note caused by the use of alternating current for heating the cathode of thermionic tubes, and

6 has for its object to provide such a method and means whereby the note caused by the alternating cathode heating current is compensated by using a rectified current of the same frequency to supply the anode.

Other objects will be apparent from the following description and claims when taken with the accompanying drawing in which Fig. 1 is a schematic representation illustrating my invention, and;

Fig. 2 illustrates a modification.

Electron tubes whose cathodes are heated by alternating current ordinarily cause a tone of the alternating current frequency and also of double the frequency in the output clrcuit. It is all the same Whether the electron tube is used as an amplifier or as an oscillation generator. In the latter case the generated oscillation is modulated by the tones caused by the heating current. Means for diminishing these tones caused by the heating current are known. A very suitable arrangement is, for instance, to arrange an ohmic resistance in parallel to the heating filament and to use the middle of this resistance as the K-point, thatis, the connection contact of the grid circuit and of the anode circuit. That component of the heating current note which has the same frequency as the heating current can be completely eliminated by this connection.

On the other hand, a heating current note of the double frequency remains. This note is based upon two causes: Firstly, the heating of the filament and consequently the electron emission slightly pulsates-in the rhythm of double the heating current frequency, even when an alternating current of as high as 500 periods per second is, employed. Secondly, the potential of the filament in respect to the grid is varied with the double frequency, as the two halves of the filament must be regarded as symmetrical.

In case the anode voltage is generated by a rectified alternating current, the anode current itself also contains a component of the double frequency of the employed rectified alternating current, and this frequency is par ticularly strong when a two phase alternating current is led through a two-parted rectifier. So the anode current brings in the same disturbing note as the heating current, if the anode alternating current and the heating current have the same frequency. The components caused by the anode current and heat ing current will strengthen or weaken one' another according to the difference of phases of these two currents. This fact is employed by the present invention according to which the phases of the disturbing components caused by the heating voltage and by the anode voltage are compulsively and constant- 1y adjusted during the working of the electron tube, so that the two components act against one another and weaken one another.

Referring to Fig. 1, the transmitting tube a acts upon the oscillatory circuit 6 which comprises inductance 1 and capacitance 2. Inductance 1 has a portion connected in the output circuit of tube a and also a portion in the input circuit of tube a to give the necessary feed back to cause sustained oscillations. The generator 0 acting thru the transformer d supplies the heating alternating current. The secondary of transformer d is connected to the filament of the tube a to which the resistance e is connected in parallel, and the middle of this resistance is, as known, the K-point. The generator 9 produces a twophased alternating current of the same frequency as that of the heating current generator 0. This current is transformed by transformer h and rectified by'the doublerectifier i. The alternating current generators 0 and g are compulsively connected to one another by the coupling A, and it is all the same whether they have a common shaft or not. The coupling A contains an arrangement by means of which the rotors of both generators can be adjusted to any desired relative angle. The maximum turning angle corresponds to a phase displacement of 360 between the alternating currents of the two generators. Any phase angle between heating current and anode current can be adjusted by means of this arrangement. According to the invention that phase displacement is adjusted,..for which the disturbing note which, for instance, may be tested by means of an auxiliary detector circuit (not shown) hasthe least strength.

The present invention further provides, that the magnitudes of the disturbing components aresoadapted to one another that the disturbing note is eliminated as completely as possible by suitably adjusting the difference of phases. This adaptation can be attained by means of different methods. One possibility is to suitably dimension the magnitude of the capacity 9 connected in parallel to the rectifier 2'. When this capacity is equal to zero, the disturbing component caused by the anode current is largest. It becomes less at increasing capacity and disappears at infinite capacit value. That value of the capacity for w ich the amplitudes of the dis.- turbing com onents are equal to one another, usually lies etween zero and infinity, unless the heating current is exceedingly strong for anfi reasons. Y

eferring to Fig. 2, there is illustrated another method of adapting the disturbing components to one another. In carrying out this method of reducing hum which has been described in particular and claimed in detail in my copending application #207,417, July 21, 1927, the grid-cathode circuit is coupled .to the direct current anode circuit, for instance, inductively, insuch a wa that the alternating current component 0 the double working frequency which the anode direct current contains, is superimposed. on the normal rid direct current or alternating current. hereby the disturbing component which is brought in by the heating current, is compensated to a certain extent, or, more exactly, it is equalled to the component of the anode note. The right phase for which the disturbing note is a minlmum so that it will completely disappear at suitable coufiling, may be adjusted, as mentioned above,

y regulatingthe variable coupling of the generators.

The arrangement in Fig. 2 is generally the same as Fig. 1, only the direct current anode circuit now contains an inductance m and the grid circuit an inductance coil n. The sev-' eral parts of Fig. 2 are denoted by the same reference characters. as similar parts of Fig. 1.' The inductances m and n are coupled to one another by a variable coupling, the sense ofwhich can be reversed. The condenser 0 bridges over the coupling coil 01. for the high frequency flowing through the grid circuit of the tube transmitter. The arrangement is adjusted in such a way that first the coils m and n are short-circuited and the phase between the working anode current and the heating current is adjusted to make the dis turbing note a minimum by suitably regulating the coupling A; then the short-circuit is removed from the coils m and n, and then the disturbing note is further diminished or completely eliminated by suitably adjusting the sense of coupling and the coeificient of coupling. 4 In some cases it may be appropriate to adjust the phases of the disturbing components of the anode current and the grid current only partly by means of the coupling A of the generators g and c by which often only an inaccurate regulation is carried out. For the accurate regulation of the phases, fur ther impedances are inserted in the anode circuit, 'or grid circuit, by means of which an accurate phase displacement is possible. This can, for instance, be carried out by connecting a capacity 12 in parallel to the coil m, or a capacity 12 in parallel to coil n, and then nearly tuning p and m, or p and n, to the disturbing frequency. The phase regulation is based upon the knowledge that a coupled circuit near to its resonance possesses a phase varying from 0 to 180 together with the capacity. Of course, it is also possible to displace the phases of the two disturbing components by arranging any other resistances in the anode circuit or direct current grid circuit.

Having described my invention, I am entitled to all modifications thereof as fall fairly within the scope of the following claims 1. The method of diminishing the alternating current hum from thermionic valves the anode cathode circuit and the cathode heating circuit of which are energized from an alternating current source which comprises, supplying the cathode heating circuit with an alternating current of definite frequency, supplying the anode cathode circuit wlth a current derived from alternating cur-.

rent of the same frequency and adjusting the phase relationship of the two currents to oppose-each other.

2. The method of diminishing the alternating current hum from thermionic valves, the

anode cathode circuit and the cathode heat ing circuit of which are energized from an alternating current source which comprises,

supplying the cathode heating circuit with an alternating current of definite frequency,

supplying the anode cathode circuit with a current derived from alternating current of the same frequency and adjusting the phase relationship and magnitude of the two to oppose and compensate each other.

3. In radio apparatus, a thermionic valve including a cathode, grid and anode, a source of alternating current forheating the cathode, a grid cathode circuit, an anode cathode circuit, a source of alternating current potential for said anode cathode circuit of the same frequency as said cathode heating cur rent, and means associated therewith for adjusting the phase relationship of the two currents.

4. In radio apparatus, a thermionic valve including a cathode, grid and anode, a source of alternating currentfor heating the cathode, a grid cathode circuit, an anode cathode circuit, a source of potential for said anode cathode circuit derived by rectifying alternating current of the same frequency as said cathode heating current, means for adjusting the phase relationship of the two currents, and means for relatively adjusting the magnitude of the two currents.

5. In radio apparatus, a thermionic valve including a cathode, grid and anode, a source of alternating current for heating the cathode, a potentiometer connected across said cathode and to said grid, a grid cathode circuit, an anode cathode circuit, a source of potential for said anode cathode circuit of v the same frequency as said cathode heating current, and means located substantially at the source of said currents for adjusting the phase relationship thereof.

6. In radio apparatus, a thermionic valve including a cathode, grid and anode, a source of alternating current for heating the oathode, a grid cathode circuit, an anode cathode circuit, a source of alternating current potential for said anode cathode circuit of the same frequency as said cathode heating cur- 'usting the phase relarent, means for ad tionshi of the two currents, and coupling means or relatively adjusting the magnitude of the two currents.

7. In radio apparatus, a thermionic valve including a cathode, grid and anode, a source of alternatin current for heating the cathode, means, Eor connecting said grid to a point having a potential intermediate to that of the terminals of said current source, a

grid cathode circuit, an anode cathode circuit, a source of alternating current potential for said anode cathode circuit of the same frequency as said cathode heating current, means for adjusting the phase relationship of the two currents and capacitive coupling means between said anode cathode circuit and said grid cathode circuit for adjusting the magnitude of the two currents.

8. In radio apparatus, a thermionic valve having cathode, grid and anode electrodes, a source of alternating current for heating the cathode, said grid being connected to a point intermediate of the terminals of said source,

a grid cathode circuit, an anode cathode circuit, a source of potential for said anode cathode circuit derived from alternating current of the same frequency as said cathode heating' current, and means for adjusting the phase relationship of the two currents.

WALTER SCHAFFER. 

